Abstract

A compact beam splitter consisting of three branches of periodic dielectric waveguides (PDW) is designed and analyzed theoretically. Both the symmetrical and asymmetrical configurations of the beam splitter are studied. The band structure for the guided modes is calculated by using finite-difference time-domain (FDTD) method with Bloch-type boundary conditions applying in an appropriate supercell. The field patterns for the whole structure and the transmissions for the output ports are calculated using the multiple scattering method. By utilizing the co-directional coupling mechanism, the light injected into the input branch can be efficiently transferred into the two output branches if the phase matching conditions are satisfied. The coupling length is short and the broad-band requirement can be achieved. Bending loss is small and high transmission (above 95 %) can be preserved for arbitrarily bent PDW if the bend radius of each bend exceeds five wavelengths. This feature indicates that the periodic dielectric waveguide beam splitter (PDWBS) is a high efficiency device for power redistribution while avoiding the lattice orientation restriction of the photonic crystal waveguides (PCW).

Figures (8)

(Color on line) (a1) and (b1): The two kinds of multimode PDWs consisting of three rows of dielectric rods. The size of the supercells for calculating the band structures is a×14a. (a2) and (b2) are the calculated band structures of these two waveguides (Choosing Ly = 1.3a.). The mode patterns are shown in the insets.

(a) The structure of the PDWBS. It consists of an input waveguide, the coupling section (b), two S-shaped waveguides (c), and two output (straight) waveguides. The coupling section is denoted by the solid line rectangle in (a), and its length is Lc. The Pi and Pa,b are the input and output power evaluated at the planes indicated in the figure, respectively. The band radius is chosen as R = 19.1a and the bend angle θ is arbitrary.

(Color on line) The one-arm transmission spectrum for the symmetric PDWBS as function of splitting angle. The horizontal and vertical axes are the reduced frequency a/λ and the splitting angle θsp, respectively.

(Color on line) The transmission spectra Ta,b(ω) for the asymmetric configuration of the PDWBS as functions of θb, taking θa to be fixed. Here “a” and “b” stand for the Arma and Armb, respectively. For θa = 0°, the calculated Ta(ω) and Tb(ω) are plotted in (a1) and (b1). For θa = 90°, the results are plotted in (a2) and (b2).

(Color on line) The field distribution (real part) around the coupling section of the symmetric PDWBS. This result is obtained by using the FDTD method. The structure and simulation parameters are the same as that used in Fig. 7(a).